Field of the Invention
The present invention relates to a power supply unit and a multi-wire electrical discharge machining apparatus, and more particularly, to a technology of reducing a variation in contact pressure between a power supply terminal, which is brought into contact with a wire group including a plurality of turns of a wire arranged in parallel at a time, and the wire group.
Description of the Related Art
In recent years, there has been developed a method of simultaneously cutting a material to be machined such as a semiconductor material, a solar cell material, and a hard material into a plurality of pieces by electrical discharge machining within a short period of time.
For example, in order to cut the material to be machined into thin plate-like pieces, a wire electrical discharge machining apparatus controls a wire to run while applying a voltage to the wire through a power supply terminal and brings the material to be machined closer to the wire to cause an electrical discharge phenomenon. In this manner, electrical discharge machining is performed on the material to be machined.
In Japanese Patent Application Laid-Open No. 08-19920, there is a description that a power supply terminal having a cylindrical shape or a columnar shape is used and an outer circumferential surface thereof is used as a contact position with a wire electrode.
Further, in Japanese Patent Application Laid-Open No. 04-105821, there is disclosed a power supply terminal made of a material having a small electrical resistance such as copper or brass, which includes a plating layer made of a hard material formed on a surface of the material having a small electrical resistance.
The wire electrical discharge machining apparatus respectively disclosed in Japanese Patent Application Laid-Open Nos. 08-19920 and 04-105821 are both single-wire electrical discharge machining apparatus.
On the other hand, in a multi-wire electrical discharge machining apparatus using a power supply terminal that is brought into contact with a wire group including a plurality of turns of a wire arranged in parallel at a time to supply a voltage to the wire group, a contact pressure between the power supply terminal and the wire is varied unless the power supply terminal and the wire group are arranged in parallel to each other and are brought into contact with each other in the parallel state. In this case, there is a fear in that power cannot be stably supplied to the wire.
Further, if the power supply terminal is pressed hard against the wire so as to stably supply the power to the wire, the degree of wear of the power supply terminal or the degree of damage of the wire disadvantageously increases. Thus, it becomes difficult to perform stable electrical discharge machining for a long period of time.